The first of these underpinnings has to do with what it means to know. As noted previously, for Lonergan knowing is not like looking. The answers are not given in the data. Rather, one infers the answers from the data. One does this by first attending to the relevant data, which in our case would consist of the biblical accounts of the exodus, the place of Moses and the exodus in Israelite and subsequent tradition, our knowledge of slavery in New Kingdom Egypt, our knowledge of Late Bronze Age southern Canaanites, other ancient Near Eastern material such as that relating to the Hyksos, etc. Few people are specialists in all of this material (and in fact I'm a specialist in none of it), so one must generally rely upon the work of specialists in these different areas. That in turn demands a degree of trust in and thus goodwill towards others (and thus we see that the conversion to love that Lonergan describes as "religious conversion" is--while perhaps not strictly necessary for the historian to carry out her or his work--a significant boon, for love excludes the paranoia that undercuts the trust and goodwill necessary for successful historiography). Attending to these various data, one then strives to understand the ancient world. One considers the various explanations that one might offer for the totality of the data. Then, one considers the conditions that must be present in the data before one can affirm any given hypothesis. Insofar as those conditions are met, one can reasonably affirm the hypothesis, and insofar as those conditions are not met one cannot. Ideally by this point one finds that one and only one hypothesis satisfies all necessary conditions for its affirmation, but when one finds a plurality of such hypotheses one must take on the harder work of adjudicating between possibilities.
The second underpinning has to do with the notion of the level of our time, to which the title "Exodus in Our Time" alludes. This was a favourite phrase of Lonergan's, and has come in some senses to sum up the entirety of his project. The idea of the level of our time is built upon the recognition that insights lead to further insights and that this process extends trans-generationally in time. We today discover that A is true. This leads our successors to discover that B is the case. This leads their successors to discover that C is the case. Eventually, after hundreds or thousands of years Z is discovered to be the case, even though by this point Z might evince little to no obvious relation to A. Such is my argument regarding the world-historical significance of the exodus. I would argue that the insight into human dignity implicit in the phrase "Let my people go!" became the genesis of a long, extended, process of insight building upon insight that has eventuated in our modern understandings of human rights and freedoms (and presumably will continue to make its presence felt for some time yet to come; we, after all, are not the telos of history). No, the exodus is not predicated upon such modern understandings. No, such modern understandings are absent from the balance of the biblical corpus, Jewish and Christian (the writers of these texts were not, after all, moderns). But, absent the exodus and absent the experiences that generated and are transmitted by these scriptures, we would not have arrived at our modern understandings of human rights (or, if we did, the path getting here would have looked quite different).
There is a reason then that the phrase "Let my people go!" has such resonance with us. It represents an insight foundational to what we as a species are becoming. The historian's joyous privilege is to investigate more closely the origin and impact of this insight.